Antenna for radiating elliptically polarized electromagnetic waves



ANTENNA FOR RADIATING ELLIPTICALLY POLARIZED ELECTROMAGNETIC WAVES FiledJuly 19, 1952 INVENTOR. FIG.2 STANLEY A. PRYGA BY W4 4% ATTORNEY UnitedStates Pate ANTENNA FOR RADIATING ELLIPTICALLY POLARIZED ELECTROMAGNETICWAVES Stanley A. Pryga, Bellflower, Calif., assignor to North AmericanAviation, Inc.

Application July 19, 1952, Serial No. 299,847

Claims. (Cl. 343-729) This invention relates to airborne antennae, andparticularly to an airborne beacon antenna adapted to propagateelliptically polarized electromagnetic waves over a substantiallytoroidal pattern with a minimum axial ratio of ellipticity.

To propagate an elliptically polarized electromagnetic wave it isnecessary to launch an electromagnetic wave which is plane polarized inone direction simultaneously with a wave, plane polarized in a directionnormal to the polarization of the first wave. Various devices exist forlaunching such waves with the proper direction such, for example, as thedipole for propagating electromagnetic waves with polarization parallelto the axis of an antenna and the slot for propagating electromagneticwaves of polarization normal to the axis of an antenna. One such schemeis disclosed in patent application Serial No. 264,481 filed January 2,1952, in the names of Robert Krausz and Donald Margerum, for AirborneBeacon Antenna. If the two Waves are launched from two different pointsin space, there is a good probability that the ellipticity of theresultant wave will not be uniform throughout the propagation pattern,i. e., the axial ratio of ellipticity (the ratio of the major to theminor axis of the ellipse) may be of an acceptably low value only withincertain small solid angles subtended from the antenna. This inventioncontemplates means for radiating elliptically polarized electromagneticwaves of substantially constant axial ratio of ellipticity oversubstantially all of a toroidal propagational radiation pattern. Thisinvention further contemplates the superposition of an array ofespecially designed slots, and a dipole to achieve the simultaneousradiation of the two plane polarized waves.

It is therefore an object of this invention to provide a beacon antennaadapted to propagate elliptically polarized electromagnetic waves.

It is another object of this invention to provide a beacon antenna forpropagating elliptically polarized electromagnetic waves ofsubstantially constant axial ratio.

it is another object of this invention to provide a beacon antenna ofrelatively uniform propagational characteristics.

Other objects of invention will become apparent from the followingdescription taken in connection with the accompanying drawings, inwhich:

Fig. 1 is an elevational view of the invention, partly in section, and

Fig. 2 is a sectional view of the device shown in Fig. 1 taken at 2-2 inFig. 1.

Referring to Fig. 1, a coaxial wave guide, including an outer conductor1 of generally cylindrical shape and an inner conductor 2, is surroundedby a fitting 3 which carries an envelope 4 of glass or some other lowdielectric constant material. Fitting 3 also carries skirt member 5 ofhollow cylindrical shape, which abuts against fitting 3 and is open atthe upper end. Outer conductor 1 terminates at circumferential slot 6,while inner conductor 2 is connected to dipole 7 which is constructed ofconducting 2,727,232 a n a Dec. 13, 1955 material such as a metal, andwhich carries four slots 8, 9, l0, and 11, each shaped like the letterJ. Dielectric collar 12 separates conductors 1 and 2, and is ofgenerally hollow cylindrical shape, with a cut-out in its lower endshaped like the frustum of a hollow cone. Each of the J -shaped I slotsincludes a vertical portion 13, a horizontal portion 14, and a tipportion 15.

In operation, electromagnetic energy is furnished by the coaxial waveguide and is end-fed to the dipole by means of conductor 2. A portion ofthe energy is therefore radiated with polarization parallel to theprincipal axis of the antenna, as shown in Fig, 1. However, due to thepresence of slots 8, 9, 10, and 11 a portion of the energy is alsoradiated with polarization normal to the principal axis of the antenna.Skirt member 5 acts as a choke to prevent the flow of currents on theoutside of the conductor below slot 6. Currents flow on the outersurface of dipole 7 and excite slots 8, 9, 10, and 11 which then radiateelectromagnetic waves with polarization normal to the axis of the waveguide. Excitation of the slots occurs at horizontal portion 14 of theslots. The effective center of radiation for the waves radiated by thedipole is very near this point, so that by proper choice of slot widthand length the resultant wave is elliptically polarized. Dipole 7 isconstructed to be approximately one-half the length of theelectromagnetic waves being propagated, and portion 13 of the slots isof very nearly the same length. Portion 15 of the slots is made to besomewhat less than one-fourth the wave length of the energy beingpropagated.

The resultant radiation pattern is of toridal shape, and the resultantwaves are elliptically polarized with an axial ratio of less than 2:1substantially throughout the pattern. Envelope 4 is provided to protectthe elements of the invention and to minimize drag when the invention isutilized on a high-speed aircraft.

Although the invention has been described and illustrated in detail, itis to be clearly understood that the same is by Way of illustration andexample only and is not to be taken by way of limitation, the spirit andscope of this invention being limited only by the terms of the appendedclaims.

I claim:

1. A microwave radiator comprising a section of coaxial wave guide,means for feeding microwave energy to said guide, means for radiating aportion of said energy out of said guide with electric field orientationin the plane of the longitudinal axis of said guide, including a dipoleat the end of said guide and a means for radiating out of said guide aportion of said energy with electric field orientation in a plane normalto the axis of said guide and in phase quadrature with said parallelpolarized energy, including a plurality of diametrally opposed slots insaid dipole, said slots being cut in the surface of said dipole withorientation parallel to the axis of said dipole.

2. An airborne beacon antenna comprising a section of coaxial waveguide, a dipole end-fed from said wave guide, a plurality ofsymmetrically disposed J-shaped slots cut in said dipole with the legsof said J parallel to the longitudinal axis of said dipole and with thehorizontal portion of the said letter J near the inboard end of saiddipole whereby said dipole radiates electromagnetic waves withpolarization in the plane of the said axis of symmetry of said waveguide, and said slots radiate electromagnetic waves with polarization ina plane normal to said axis to thereby propagate elliptically polarizedelectromagnetic waves in a substantially toroidal pattern.

3. The device as recited in claim 2 and further comprising a hollowcylindrical conducting choke attached to said guide near said dipole toprevent circulating currents on the outside of said guide.

4. In a microwave antenna having a radiating element radiating planepolarized microwave radiation, means for producing an electric fieldwith polarization normal to that produced by said element, comprising aJ-shaped slot in said element oriented with its axis in the plane ofsaid radiation of said radiating element. I Y i 5. In a microwaveantenna having a cylindrical dipole, radiator means for producing anelectric field with polarization normal to the axis of said dipoleradiator, comprising a J-shaped slot in said dipole radiator orientedwith 10 its axis parallel to the axis of said dipole radiator.

References Cited in the file of this patent UNITED STATES PATENTS2,412,320 Carter Dec. 10, '1946 Riblet Jan. 6, 1948- Lindenl lad Oct. 6,1948 Cork et a1. Jan. 18, 1949 Gilbert Aug. 16, 1949 Riblet July 31,1951 Smith Jan. 5, 1954 FOREIGN PATENTS Great Britain Sept. 29, 1947Great Britain July 11, 1951 Great Britain Jan. 2, 1952

